Long-term exposure to air pollution has increasingly been linked to strokes, which affect almost 800,000 Americans each year.

Now, a meta-analysis of 110 studies involving more than 18 million cases of stroke shows short-term exposures pose heightened risks, too.

The paper appears in Neurology, the medical journal of the American Academy of Neurology.

Five days: That’s all it takes for high levels of some air pollutants to raise the risk of stroke, whether it’s a 5% uptick from high ozone levels or a more than 26% surge for high concentrations of carbon monoxide and nitrogen dioxide (NO2).

Stroke risk from sulfur dioxide, another byproduct of fossil fuel burning, fell in the middle (15%), but the pungent gas raised the likelihood of death from stroke 60%.

Higher concentrations of NO2 correlated with a 33% increase in death risk.

High levels of particulates like PM10s and PM2.5s raised the risk of stroke around 15% and increased stroke mortality risk 2% and 9%, respectively.

PM numbers refer to particle sizes, measured in microns, or millionths of a meter.

Examples of PM2.5s or smaller include specks from car exhaust, power plant and industrial emissions, and forest and grass fires. PM10s comprise grains of dust from roads and construction sites.

According to the Arizona Department of Environmental Quality, Phoenix had no five-day spans related to PM10s and PM2.5s over the past year.

The city did see five five-day periods of high ozone, however: two last summer and three this summer.